Some of this is cultural. Some of it is biological. Now it's about laws.
Some of this is about governments with unlimited budgets that do not have to prioritize what legal actions to take.
And some in the "old days" were victims of overlooked abuse. Now when I see a 21 year old guy around 15 year old girls I just think creepy loser. Go find somebody your own age! You can seem like a “decent” guy but why were you prowling around 15 year olds in the first place? A 21 year old is junior in college age, 15 or 16 is tenth grade. Yuck!
“My first ex-wife’s grandmother was 13 when she got married on a North Texas prarie.”
Laura Ingalls Wilder spoke of such things in her books. I suppose it happened. Consider 13 year olds were doing hard work in the house it really did not matter if they got married at 13 back then.
Back then. It is 2012 and most 13 year olds are not running a farm.